The adults in this world who worry about children are more worried than ever.

That, of course, should be no surprise: In hard times when resources are limited and social programs in general are at risk, those for children are even more so. "The payoff," says James R. Grant, executive director of the United Nations Children's Fund, which today celebrates its 36th birthday, "is so much slower.

"Although we're at the end of 35 years of unprecedented progress for children, for the first time in the post World War II era, that progress is now under challenge."

In response to that challenge, representatives of UNICEF, other U.N. agencies, the World Health Organization, World Bank, World Food Council, among others, have been brainstorming for some months to find a way to continue the progress that has seen "a greater reduction of child mortality, greater improvement of health . . . in the last 35 years than in the preceding 500 to 1,000 years."

They think they have found a way even, as Grant puts it, "in these dark times."

Based on a series of medical breakthroughs, along with 3 1/2 decades of intense field work and educational programs, UNICEF and its fellow agencies are today unveiling--internationally -- a "State of the World's Children" program they optimistically expect to create as great a revolution in worldwide child care as the so-called "green revolution" of the 1960s and '70s did for worldwide agriculture.

The four-pronged program (aimed mainly at developing nations, but also useful in rural and urban areas of the so-called developed) is dependent on a delivery system that has been burgeoning over the past decades: ranging from the training and placement of village health workers--100,000 in India alone--to the proliferation of communication devices as simple as the battery-operated transistor radio.

The program is called GOBI, an acronym for its concerns: growth charts, oral rehydration therapy, breast-feeding and immunization. It is the oral rehydration therapy (ORT) and the immunization that contain the potential for dramatic and immediate medical impact on the most children.

Oral rehydration is a medical term for the restoration of vital fluids lost by infants and young children with diarrhea: the direct cause of about 5 million children's deaths a year, and indirect cause of millions more because of lowered resistance and malnutrition.

Within the past decade--borrowing in part from a Southeast Asian folk remedy -- medical science has discovered that fluids administered by mouth can be absorbed by the diarrhea-ridden small bodies only when a formulation of salts and sugar accompanies the liquid, restoring both fluid and electrolyte balance. A pre-mixed packet of six parts sugar to one-half part salt, is now available, inexpensive and ready for international distribution. It need only be mixed with water to perform its lifesaving function.

Along with the development of the ORT packets come vaccines that no longer require constant refrigeration -- until now a major deterrent to providing the world's children with immunities to polio, diphtheria, tetanus, whooping cough, measles . . .

Those are the contributions of science.

But so simple a thing as a return to breast-feeding -- disastrously undermined in the past decade or so by misleading and incomplete information touting the virtues of prepared formulas -- can be part of the children's health revolution. An even simpler concept -- the individualized growth chart for each baby -- can be a tool for modifying the habits of a village mother. It is a lure to bring her into regional clinics where inadvertent malnutrition can be spotted on the chart, where a baby can receive second and third immunization shots when needed, where the mother can learn about such things as family spacing and proper nutrition.

It could be, says Grant, "a virtuous circle." For reasons only partially understood, as child mortality rates drop, so do birth rates, usually at an even greater rate. Part of this may be attributed to the statistically significant, although only partially effective, contraceptive effect of breast-feeding.

In any case, the program is ready to start. "You could," says Grant, "cut the death rate of children in low-income countries in half in the next 10 to 15 years for a very low cost--financial or political."

For copies of the UNICEF "State of the World's Children" report and more information on GOBI, write Information Division, UNICEF, New York, N.Y. 10017.